I have run into differences as well.
But it is not just with FireFly and SuperFly that I see this.

I use various render engines in other apps and get differences as well.
Making them work the same could also create an issue that others would notice.
That would simply be that Superfly would drastically differ from Cycles then.
So basically anyone coming to Poser that was used to Cycles would be scratching their heads asking why something looked far different than what they expected.

It is a double edged sword in many respects.

I do agree that there are some oddities that still have me scratching my head on how to get around them. Both from Firefly and a Cycles perspective.

Posers Superfly has about the same nodes for procedural textures than Firefly. They have been ported from Firefly to Superfly, they are not a part of cycles. Things like Noise, Wave, Turbulence, etc.

The scale of some of these nodes is different between SuperFly and FireFly. This is something which makes it unnessesarily hard to convert procedural textures between these renderers. From my point of view, there is no reason why the procedural nodes should not work similar in both render engines.

This makes it really difficult to convert shaders. In fact, it's more like recreating them - which also means that procedural shaders cannot be shared between the two render engines. So I hope for a fix for this in SP4, hopefully soon.

By the way, I like the fast pace for the SPs a lot. It's great to have the new scatter algorithm in SP4. Just pretty please, fix this too.